Evaluation of consolidating and water repellent treatments applied to the miocene sandstone used in Tunisian Heritage monuments

The research reported in the present paper focused on the behaviour of the Miocene sandstone used to build the Roman aqueduct at Zaghouan-Carthage and other Tunisian Heritage monuments, after application of water repellent and consolidating treatments as a preliminary to restoration. Commercial consolidants and water repellents were used in the experiments: two ethyl silicate consolidants, Tegovakon (TV) and Keim-Silex OH (KSOH); two (siloxane) water repellents, Tegosivin THE 328 (THE) and Tegosivln HL100 (THL); and a dual (consolidant and water repellent) action substance, Keim-Silex H (KSH) (silicate acid ester base with siloxane). A mixed treatment consisting of successive coats of TV and THL (TVHL) was also applied. These organosilicate consolidants and water repellents acted on the porous structure of the sandstone, reducing total porosity and water vapour permeability. The water repellent THE was found to affect these properties least, with a pore size distribution that resembled the distribution in the untreated sandstone most closely. Water repellents diminish water absorption and consolidants increase mechanical strength. The TV-THL mix, which yielded results similar to those obtained with water repellents alone, was unable to prevent the substantial scaling that occurs during (RILEM) salt crystallisation-induced artificial ageing. The best results were found with the dual action consolidant/ water repellent product (KSH), which improved the mechanical properties while affording protection from the decay caused by salts in artificial ageing trials. This substance was found to reduce water vapour permeability, however.